buildkite is leaps and bounds above the others. especially if you need to really tailor your workloads to the change diff (say in a monorepo), the dynamic pipeline support is superb.
really surprised there are no others though. dagger.io was in the space but the level of complexity is an order of magnitude higher
Github Actions is actually one of the better CI options out there, even if on an absolute scale it is still pretty bad.
As far as I can tell nobody has made a CI system that is actually good.